1. Field of the Invention
This invention relates to lead-acid batteries having gelled electrolytes and methods for making such batteries.
2. Description of the Prior Art
Gelled electrolyte lead-acid batteries are known and have been available for commercial use since the early 1920's, as evidenced by the May 15, 1921 issue of The Commercial Car Journal, page 102.
Of the patent prior art, U.S. Pat. Nos. 1,389,750; 1,416,195; 1,417,007; 1,572,586; 2,483,868; 3,305,396; 3,257,237; 3,457,112 and 3,711,332 are known to applicant. Other patent prior art known to applicants includes U.S. Pat. Nos. 2,631,117; 3,202,611; 3,257,237; 3,271,199; 3,305,396; 3,328,208; 3,457,112; 3,506,750; 3,556,860; 3,578,504; 3,709,737; 3,716,412; 3,765,943; 3,776,779; 3,885,988; 3,904,434; 4,140,840; 4,147,843; 4,150,199; 4,238,556; 4,039,462; 4,288,913; 4,317,872; and 4,414,302. Of these, 3,711,332 is most relevant to the apparatus aspect of this invention while 2,483,868 and 3,305,396 are most relevant to the method aspect of this invention.
Concerning the apparatus aspect of the invention, 3,711,332 discloses utilizing a ratio of sulfuric acid to aqueous sodium silicate solution (Na.sub.2 SiO.sub.3) of from 6:1 to 10:1 to form the electrolyte gel, with the ratio of sodium silicate to water forming the aqueous sodium silicate solution being about 1:1. Sodium silicate, Na.sub.2 SiO.sub.3, as disclosed and taught by 3,711,332, is conventionally referred to as "water glass."
3,711,332 uses electrolyte which forms a liquid phase above the gel phase in the battery, with the two phase system (consisting of the liquid and the gel) changing proportions during battery operation. The liquid phase enters the gel phase during battery discharge and reemerges from the gel phase during battery charging. Depending upon the assumption used for the specific gravity of the sodium silicate and the resultant sodium silicate solution, the ratio of sodium silicate to sulfuric acid ranges from 5.5 to 9.1 in 3,711,332 (for sodium silicate specific gravity of 2.4), ranges from 14.6 to 19.4 in 3,711,332 (for sodium silicate specific gravity of 1.4) and ranges from 10.9 to 18.2 in 3,711,332 (for sodium silicate specific gravity of 1.2).
U.S. Pat. No. 2,483,868 discloses production of 94% anhydrous silica gel at column 1, line 4. Silica, as sodium silicate solution, is sprayed into sulfuric acid to form a sol which turns to a gel as taught at column 2, line 7 of '868. As high as 17% silica results. The sulfuric acid is maintained in a baffled tank.
U.S. Pat. No. 3,305,396 recites that it is known to produce colloidally dispersed silicon as silicic acid for use in dry electrolytes, having a silica particle size of five (5) to twenty (20) microns or less, as taught at column 1, lines 26 and 31. '396 relates to dry cells with electrolytes consisting of sulfuric acid with colloidal silicic acid, as taught at column 1, line 60. A thixotropic electrolyte consisting of sulfuric acid and colloidally dispersed silicic acid is reduced to liquid in a high speed mixer and introduced into the cell housing in an evacuated space, as taught at column 1, line 69. The silicic acid is produced by the pyrogenic method from silicon tetrachloride and is free from alkaline substances, as taught at column 3, line 5.
U.S. Pat. No. 2,631,117 discloses a battery additive product and process. The process includes pulverizing an alumino-silicate shell and mixing the pulverized product with hot sulfuric acid to facilitate extraction of occluded soluble portions. The mixture is then filtered while hot and added to a hydroxide to alkalize the mixture and precipitate the ions to form an insoluble hydroxide. The precipitate is separated by filtration and acidified to convert dissolved salts to free acids and then concentrated to form the product. Addition of the alumino-silicate shell to the electrolyte maintains lead sulfate in suspension and prevents it from precipitating on to the surface of the plates.
U.S. Pat. No. 3,202,611 discloses a thixotropic electrolyte for an electrolytic capacitor, which is particulate silica in the 0.015 to 0.020 micron range in a solution of acid containing 5-8% by weight of particulate silica to 92-95% by weight of acid. The acid is preferably sulfuric or hydrochloric acid.
U.S. Pat. No. 3,271,199 discloses a gelled storage battery electrolyte including a solution of aqueous sulfuric acid, pectin and colloidal silica. The electrolyte preferably contains about 0.3% of pectin by weight of the sulfuric acid solution. The pectin and colloidal silica are mixed in a dry state and then the mixture is combined with the sulfuric acid electrolyte.
U.S. Pat. No. 3,328,208 discloses a lead storage battery and process of making a lead storage battery with a solidified electrolyte.
The process includes intimately mixing pulverulent dry pectin and a supporting material such as natural rubber, synthetic rubber or thermoplastic materials having a softening point below the decomposition temperature of pectin, processing the mixture to foils, sandwiching the foils between electrode plates and impregnating the foils with battery acid in an amount sufficient to produce a swollen pectin gel.
U.S. Pat. No. 3,457,112 discloses a lead-acid storage battery including lead electrodes of opposite polarity being free of antimony with an active lead mass supported by the electrodes. A nonfluid electrolyte is interposed between and contacting adjacent electrodes, with the nonfluid electrolyte consisting of a mixture of aqueous sulfuric acid and a thickening agent. The thickening agent compound should be present in an amount in excess of 0.2% of the weight of the aqueous sulfuric acid. Sufficient thickening agent is added to render the electrolyte nonfluid.
U.S. Pat. No. 3,506,750 discloses manufacture of galvanic cells containing coaxially disposed positive and negative electrodes with current conductors and an ion conducting diaphragm separating the electrodes. The method includes subjecting the electrolyte to preliminary gellingfollowed by simultaneously pressing in and molding the pregelled electrolyte and at least one electrode into the casing of the galvanic cell.
U.S. Pat. No. 3,556,860 discloses a storage battery and electrolyte precursor. The invention includes a sulfuric acid gel formed by incorporating the reaction product of oxides of boron and phosphorous into sulfuric acid. The sulfuric acid is a concentrated sulfuric acid having a concentration of at least about 95%. The invention also includes gelation of the sulfuric acid which contains free oleum or sulphur trioxide up to about 30%.
U.S. Pat. No. 3,578,504 discloses a method of activating a silver oxide-zinc primary cell. The method includes mixing together 5-40 weight percent of magnesium oxide powder in an aqueous alkaline electrolyte to form a pourable electrolytic solution. The assembled cell is filled with the electrolytic solution through a vent opening and then closed to allow the viscosity of the solution to increase to form a gel prior to discharging the cell to prevent silver migration after discharging.
U.S. Pat. No. 3,709,737 discloses a leak proof battery and method of manufacturing the same. The method of the invention includes forming a mixture of thermoplastic synthetic resin powder and hydrated silica gel around an assembly of positive and negatives plates, enclosing the composition and plates and heating the same in steam at a temperature above 100.degree. C. in order to soften and melt at least a portion of the resin powder, solidifying the resin to form a liquid absorbable porous body integral with the negative and positive plates, impregnating the absorbable porous body with an electrolyte and inserting the absorbable porous body and the positive and negative plates within a battery container.
U.S. Pat. No. 3,716,412 discloses a lead-acid battery wherein the electrolyte contains sulfuric acid, water and silica. The electrolyte contains 5-30 grams of amorphous silica per liter of electrolyte and the resulting composition is non-thixotropic. Interestingly, '412 teaches that at higher concentration of silica to sulfuric acid electrolyte, specifically above 100 grams of silica per liter, the electrolyte thickens significantly and has a thixotropic property which '412 notes "appears to reduce the materials ability to wet the separators and the active material and thus reduces the battery's performance." (Column 3, lines 10-12).
U.S. Pat. No. 3,765,943 discloses a process for fabrication of positive electrodes for lead-acid batteries wherein the electrodes are fabricated from grids filled with paste and including the steps of reacting lead oxide in an aqueous suspension with sulfuric acid at 80.degree.-100.degree. C. to produce tetrabasic lead sulfate. The lead-containing material contains lead oxide of at least 90% by weight of an orthorhombic modification, the aqueous suspension in which the reaction takes place is preacidified to a pH range of 1-3.5 prior to the addition of lead oxide and the tetrabasic lead sulfate is separated from the aqueous suspension within one hour after complete addition of the sulfuric acid.
U.S. Pat. No. 3,776,779 discloses a battery electrolyte containing a polyglycol polymer. The electrolyte is gelled by silica and a polyethylene glycol polymer in a small but effective amount to serve as a stabilizer for the electrolyte, which is adequate to render the electrolyte non-thixotropic, i.e. solid as opposed to viscous, and which also serves to decrease the tendency of gelled electrolyte to physically break down by cracking and shrinking during battery use.
U.S. Pat. No. 3,885,988 discloses a method for filling adjacent insulating tubes forming a positive plate of a lead-acid storage battery. The method includes adding supplementary water to a paste-like mixture to reduce the viscosity to form a suspension with the water serving as a carrier for the paste. Then the suspension is rapidly injected under pressure into the tubes before the supplementary carrier water separates from the suspension. The suspension is injected in sufficient quantity to provide the predetermined volume of paste for the battery tubes, with the supplementary water then being separated from the paste-like mixture and from the suspension. The suspension preferably consists of lead oxide dust, red lead, sulfuric acid and water.
U.S. Pat. No. 3,904,434 discloses a sealed lead storage battery which uses lead having an equilibrium potential electrochemically more negative than hydrogen and lead oxide as a positive electrode active material. The electrolyte of the battery is a gel obtained by adding 20% silica sol concentrated sulfuric acid in a proportion of 2 cc per 1 gram of SiO.sub.2.
U.S. Pat. No. 4,140,840 discloses a lead-sulfuric acid storage battery having grids supporting the cathodic and anodic reactants of the cell, with at least one of the grids comprising a base of one of the metals iron, nickel, stainless steel and alloys of iron and nickel. The base has a coating of tin-nickel alloy. Positive grids within the battery have an outer layer of lead peroxide constituting the cathodic reactant, a gelled electrolyte of sulfuric acid and an encapsulating epoxy resin hermetically sealing the battery.
U.S. Pat. No. 4,147,843 discloses an electrolyte precursor composition for use in galvanic batteries wherein the electrolyte flows as a liquid solution. The composition includes a paste-like mixture of concentrated sulfuric acid and powdered chromic acid.
U.S. Pat. No. 4,150,199 discloses a precursor for an electrical storage battery including a positive and negative plates between separator plates. Each separator plate consists of a densely compressed compact containing 70-100% of silica capable, when soaked with a liquid electrolyte, of forming a pressure-resistant gel and 0-30% of acid-resistant and oxidation-resistant fibers, typically polyester. The precursor converts into an operative storage battery upon introduction of sulfuric acid electrolyte into the housing whereupon the silica combines with the acid to form a gelled separator.
U.S. Pat. No. 4,238,556 discloses a lead acid cell having a lead negative electrode, a lead dioxide positive electrode and an electrolyte consisting of a sulfuric acid solution having a cellulosic catalyst dissolved therein to prevent sulfation of the electrodes. The catalyst is preferably nitrocellulose, cellulose nitrate or camphor.
U.S. Pat. No. 4,038,462 discloses a solid-electrolyte battery with a multiplicity of anode and cathode spaces forming electrode spaces arranged in parallel in straight lines attached to collecting spaces and alternately disposed in an iron conducting body of solid electrolyte. The electrode spaces have adjacent electrode spaces of opposite plurality wherein the anode spaces comprise a set of hollow recesses, in the body of the solid electrolyte, forming anode channels closed at one end and open at the other end to a first collecting space in the body of the solid electrolyte. The cathode spaces comprise a second set of hollow recesses in the body of the solid electrolyte, forming cathode channels closed at one end and open at the other end to a second collecting space disposed in the body of the solid electrolyte. The first and second collecting spaces having locking lids.
U.S. Pat. No. 4,288,913 discloses a method of forming in situ gelled anodes. The method includes mixing a powdered anode metal with a gelling agent and with liquid means other than the gelling agent for maintaining, during subsequent gelling, a homogenous mixture of the powdered metal, the gelling agent and a liquid. The gelling agent is capable of gelling the powdered anode metal when in the presence of an aqueous electrolyte solution. The resulting ungelled mixture is dispensed into an electrolyte solution in an electrochemical cell, whereby the substantially homogeneously gelled anode is formed in situ.
U.S. Pat. No. 4,317,872 discloses a lead-acid battery with gel electrolyte. The battery includes a container, a plurality of alternating positive and negative electrodes and separators between the electrodes. The separators include a silicate component mixed with an oxygen compound of boron to form a microfibrous mat. The battery also contains a gel electrolyte in substantial physical contact with the positive and negative electrodes and separators in each cell. The electrolyte has a sulfuric acid component and an SiO.sub.2 silica component derived from an aqueous colloidal dispersion of silica (SiO.sub.2) particles with a means causing a negative electric charge on the surface to cause the particles to repel each other and catalyze the formation of a siloxane cross linkage, having each atom of silicon bonded to four (4) atoms of oxygen, i.e. SiO.sub.4.
U.S. Pat. No. 4,414,302 discloses a method of making a lead storage battery. The battery includes a thixotropic gel electrolyte consisting substantially of sulfuric acid and a silicon dioxide gelling agent. The electrolyte may also include a small portion of orthophosphoric acid which electrochemically bonds in the active material of the electrodes. The battery thereafter is filled with the gelling agent and sulfuric acid.
Prior art practice includes using solid fumed silica (SiO.sub.2) and combining that with H.sub.2 SO.sub.4 in a mixing process which takes about 12 hours and pouring the resultant slurry into a dry charged battery. This process is exceedingly time consuming and expensive.
Aqueous dispersions of colloidal alkali metal silicas are known for use as binders in ceramic investment shell casting and foundries with alcohol being combined with the aqueous colloidal dispersion when faster shell drying and earlier green strength is desired. Using an aqueous colloidal dispersion of an alkali metal polysilica, specifically sodium polysilica, results in ceramic investment shell castings having very smooth surfaces and very close design tolerances.
In the past, some artisans have mixed dry fumed silica with sulfuric acid to provide a gel for introduction into a lead-acid battery precursor. This mixing procedure is quite time consuming, typically taking from 18 to 24 hours for mixing. The dry fumed silica is very fine, making it very difficult to handle. The dry fumed silica-sulfuric acid blend is difficult to keep sufficiently liquid so that the blend flows easily enough to be introduced into the battery precursor. In this prior practice, the fumed silica blend material is converted into the gel form before being introduced into the battery; the thixotropic characteristic of the gel blend material makes it feasible to hold the gel in a liquid condition through continuous mixing and to introduce it into the battery, but with some difficulty.